This sentence is grammatically correct, but it is a weird way to express yourself. Unless you mean something specific, this is not the best way to say it. The way that you have written it right now is weird because it comes across as almost part of a mandate.
The reason that you will not be at home tomorrow is part of a code, or a set of rules. You can liken it to the ten commandments from the Bible, for instance, which include commandments such as “thou shall not kill” or “thou shall not commit adultery”.
The way that you have written this sentence reminds me of this kind of rule.
A better way to word this is to get rid of “shall”. Even though it might sound more formal, it is really not appropriate unless you are trying to control or limit someone.
Do not be afraid to use simpler vocabulary, as getting a clear message across is much more sophisticated than confusing anyone that you are talking to. A couple of better ways to say this would include:
- I will not be at home tomorrow.
- Tomorrow, I won’t be home.
- Tomorrow, I can’t be at home.
- I should not be at home tomorrow.
